The Carter administration raised the possibility yesterday that it may go slowly in eliminating tax breaks for U.S. corporations and private citizens working abroad, in part because of fears of injuring the nation's already-shaky export posture.

Treasury Secretary W. Michael Blumenthal hinted to reporters the administration may be having second thoughts about immediate elimination of a controversial tax subsidy for exporters who establish domestic international sales corporations.

He also suggested that Treasury may want to move cautiously in deciding how to handle a protest over 1976 legislation that trimmed back special tax breaks for American citizens working abroad. That measure already has been portponed by Congress once.

The review of the provision eliminating the DISC tax subsidy represents a turnabout for the administration. Only last summer, Blumenthal was asserting publicly that the DISC provision was "unjustifiable." Carter's tax package is expected to propose engingit entirely.

But Blumenthal is reported by some officials to be considering asking Carter to defer the effective date both of that proposal and a companion measure in the tax package that would eliminate present deferral of foreign source income of corporations.

In both cases - the IDSC provision and the measure affecting U.S. citizens working abroad - Blumenthal cited the nations worsening trade picture as a key consideration in reviewing the proposals.

While acknowledging that many critics have called for elimination of the DISC benefit, the Secretary said the proposal should be considered "in terms of ur efforts at the present time to boost exports and to reduce trade imbalance, which is a very serious matter."

He also referred to export problems in discussing the second measure. Most Americans working abroad "play an important role in the sale of American products" there, he said.

"It is in our interest to make sure we have qualified American citizens who a willing . . . to do that very important job for our economy," he said.

On the provision involving Americans working abroad, the Secretary confirmed that the treasury has asked Congress to postpone any tightening in the tax treatment of U.S. citizens living overseas until next Jan. 1 - the same date approved by the House Ways and Means Committee.

The move is an effort ot buy time in order to give all sides an opportunity to agree on a compromise measure. There was no opposition when Congress tightened the overseas tax provisions last fall, but in the intervening months the law has sparked heavy protests.

On other matters, Blumenthal insisted the administration's agreemtn to delay President's tax revision package will not spoil chances of beginning congressional hearings this session, but conceded the move could leave the measure behind schedule next year.

The Secretary told his news conference that despite the postponement the tax package will be unveiled "intim for" the House Ways and Means Committed to begin hearings before adjournment. He admitted the setback could delay the start of formal.

The timing is regarded as critical, since many strategists believe that any unusual delays could snag the measure irresparably. Most analysts agree the tax proposal will have to be rushed through the House by May to have much chance of full passage next year.

Carter agreed to dalay his Oct. 3 unveiling date after Senate leaders demanded he put off the program until they act on his energy bill to prevent political tradeoffs between the two measures.

There is substantial uncertainty over just when the Senate will complete its work on the energy bill and how long the House will stay in session after that. Some congressional leaders reportedly are anxious to adjourn in mid-October.

President Carter is scheduled to make a round of final decisions on the tax package this weekend. Carter has been reviewing a packet of recommendations from Treasury officials since last Friday, but so far reportedly has not approved any specific proposal.